Qt seems like a potential fit. It covers desktop (all major platforms), Symbian, and Android support has just gone into beta (see Necessitas).

UI dev with Qt Quick 2.0 is nice and fast. "Sprites moving and turning" can be handled with QML built-in animation (it's got everything from basic transitions to particle systems) and/or integrated Javascript. For efficiency and/or anti-hacking, you might want to stick the client logic and communication in the C++ back-end. If the client logic is lightweight, you won't need much C++. You also have the option of writing logic in Javascript and sharing it with a HTML5 or other client.